The present invention relates to transmission systems for transmitting analog data on an unshielded twisted pair (UTP) of wires. More specifically, this invention is directed to an integrated gigabit Ethernet transmitter.
The past few years has witnessed an almost exponential growth in the extent of high speed data networks, and the data transmission speeds contemplated over such networks. In particular, bidirectional data transmission in accordance with the various Ethernet network protocols, over unshielded twisted pair (UTP) wiring, has emerged as the network implementation of choice for general commercial LAN installations as well as for some of the more prosaic residential and academic applications.
Local Area Networks (LAN) provide network connectivity for personal computers, workstations and servers. Ethernet, in its original 10BASE-T form, remains the dominant network technology for LANs. However, among the high speed LAN technologies available today, Fast Ethernet, or 100BASE-T, has become the leading choice. Fast Ethernet technology provides a smooth, non-disruptive evolution from the 10 megabits per second (Mbps) performance of the 10BASE-T to the 100 Mbps performance of the 100BASE-T. The growing use of 100BASE-T connections to servers and desktops is creating a definite need for an even higher speed network technology at the backbone and server level.
The most appropriate solution to this need, now in development, is Gigabit Ethernet. Gigabit Ethernet will provide 1 gigabit per second (Gbps) bandwidth with the simplicity of Ethernet at lower cost than other technologies of comparable speed, and will offer a smooth upgrade path for current Ethernet installations. With increased speed of Gigabit Ethernet data transmission, it is evident that EMI emission and line reflections will cause the transmitted signal to become substantially impaired in the absence of some methodology for filtering the transmitted data.
Therefore, there is a need for an integrated transmitter in a data transmission system for pulse shaping digital input data and reducing EMI emissions, implemented with relatively simple circuitry.
A multi-transmitter communication system is configured for transmitting analog signals over a multi-channel communication network. The system is constructed to incorporate M transmitters, each having an output for serving a transmit signal on a transmit signal path electrically coupled between each communication channel and the output of the respective transmitter. A timing circuit is electrically coupled to each transmitter for providing the required timing signals for each transmitter. The timing signals for the transmitters define a clock domain that is staggered in time resulting in a respective phase shift of the output signals of each transmitter.
In one embodiment of the present invention, the timing signals are staggered in time for predetermined time intervals to reduce aggregate electromagnetic emission caused by signal images centered around integer multiples of frequency Fi of the M transmitters. M timing references staggered in time by 1/(Fi*M) are generated by the timing circuit to drive the output of each of the M transmitters respectively. In another embodiment, each transmitter has a current-mode differential pair output for transmitting data on a UTP transmission line and the staggered timing is generated by a phase-lock-loop (PLL).